Polymers of vinyl trifluoroacetate and vinyl alcohol are known in the art.
U.S. Pat. No. 2,436,144 discloses copolymers of vinyl trifluoroacetate and olefinic compounds useful as sheet materials for wrapping, for impregnating and coating materials, and in molding applications. It is noted that optimum properties are obtained when greater than 50 percent by weight of the polymerizable mixture is vinyl trifluoroacetate. The patent claims interpolymers containing 15 to 70 weight percent of vinyl trifluoroacetate. Example VIII discloses the hydrolysis of a vinyl trifluoroacetate homopolymer with sodium ethylate to provide a polymer which is soluble in water. No examples or suggestion of solvolysis of copolymers of poly(vinyl trifluoroacetate) are disclosed.
Harris, et al., J. Polymer Sci. A-1, 4 665-677 (1966) and Haas, et al., J. Polymer Sci., 22 291 (1956), disclose the hydrolysis of poly(vinyl trifluoroacetate) homopolymers to poly(vinyl alcohol) homopolymers with syndiotactic properties (i.e., the stereochemical configurations of the tertiary carbon atoms are regularly alternating). U.S. Pat. Nos. 3,220,960 and 3,361,858 teach that contact lenses can be made from cross-linked poly(vinyl alcohol) homopolymer hydrogels.
Copolymers of vinyl alcohol are known and are reported, e.g., in Japanese Pat. No. 78/91,995 and Japanese Pat. No. 78/103,092; by L. A. Vol'f, et al., Khim. Volokna, 2, 14 (1979) and by J. Chernikov, et al., Nauchn. Tr., Kuban Gos. Univ., 243, 141 (1977). The latter discloses cross-linked graft copolymers of poly(vinyl alcohol) and poly(acrylic) acid useful as biologically active man-made fibers.
None of the above-mentioned art discloses that non-crosslinked copolymers of vinyl trifluoroacetate with less than 5 weight percent of certain comonomers can provide, by solvolysis, syndiotactic poly(vinyl alcohol) copolymers which surprisingly are insoluble in water and possess the desirable properties of very strong hydrogels. Further, it is known in the art that when cross-linked poly(vinyl alcohol) homopolymers are to be made into contact lenses they cannot be molded due to the infusibility of poly(vinyl alcohol), but they must be mechanically cut or machined into the contact lens shape after cross-linking or curing, then hydrated to form the hydrogels.